Leak detector for fluid conductors

ABSTRACT

Pipeline leaks are detected by an in-line pig like device having an orifice plate mounted at each end of a frame member and differential pressure measuring means across each orifice at each end, the output of each differential pressure measuring means is in turn fed to another differential pressure sensing means, the output of which is transmitted to a recording means whereby a leak is detected when the duration of any change in a signal recorded corresponds to the difference in the distance between two sealing members disposed at each end of said frame member.

United States Patent 1 McCarron Jan.1,1974

[21] Appl. No.: 285,761

[52] 0.8. Cl 73/40.5 R [51] Int. Cl. GOlm 3/28 [58] Field of Search73/405, 49.1

[56] References Cited UNITED STATES PATENTS 3,117,453 1/1964 VerNooy73/40.5 X

9/1968 Cramer 73/40.5 10/1970 Moore et a]. 73/40.5 X

Primary Examiner-Richard C. Queisser Assistant ExaminerJoseph W. RoskosAttorney-Theodore E. Bieber et al.

[ 5 7 ABSTRACT Pipeline leaks are detected by an in-line pig like devicehaving an orifice plate mounted at each end of a frame member anddifferential pressure measuring means across each orifice at each end,the output of each differential pressure measuring means is in turn fedto another differential pressure sensing means, the output of which istransmitted to a recording means whereby a leak is detected when theduration of any 2,782,370 2/1957, change in a signal recordedcorresponds to the differ- 5 l /1960 ence in the distance between twosealing members dis- 1162.505 12/1964 posed at each end of said framemember. 3,196,686 7/l965 3,382,705 5/1968 7 Claims, 1 Drawing FigureBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to an apparatus for detecting leaks in pipelines having fluidflowing therethrough and more particularly to an apparatus that passesthrough a fluid carrying pipeline, the fluid therein being underpressure, and detects leaks in the pipeline by means of measuring theduration of the change in a signal that measures the difference in flowrates between two flow sensing means mounted at the respective ends ofthe apparatus.

2. Description of the Prior Art It is known that leaks in a pipeline maybe determined to exist by sending certain acoustical or pressureresponsive instruments through a pipeline and making a continuous recordof sound or pressure as the recording instrument passes through theline. Instruments of this general type are well known and are usuallymounted in a pipeline scraper or pig of conventional type for internalsurveying of pipelines. The pig consists essentially of an elongatedbody member usually tubular in shape carrying a plurality of sealingmembers extending radially outward from the body to make a sealingcontact with the wall of the pipeline, the pig being propelled ortransported through the pipeline by flow of fluid therethrough.

It has been customary to mount instruments in the body of such pigs andsend them through the pipeline to determine the existence of leaks alongthe line. U. S. Pat. No. 3,016,733 illustrates a device of this type.The apparatus of the 9 6,723 .netsntyt lize .q rca i pressure to recordthe existence of a leak in a pipeline and does so by measuring andcomparing the pressure on a leading edge of the pig compared to thepressure between two smaller sealing elements in contact with the innerwall of the pipeline. Therefore, any pressure difference between theisolated region of the smaller packing elements and a region in thepipeline ahead of the carrier or pig will effect a motion of the pen armor recording device, and the difference in pressure is used as anindication of a leak.

Another U.S. Pat. No. 3,1 17,453 illustrates the use of differentialpressure gauges and total pressure gauges to isolate the leak in apipeline. This particular patent uses a differential pressure gauge thatmeasures the difference of pressure between the forward and trailingedge of the pig and also has two total pressure gauges, one at thetrailing edge of the pig and a second total pressure gauge betweensealing cups that isolate a portion of the line. A leak in the pipelineis indicated using the apparatus of the U.S. Pat. No. 3,117,453, bycomparing the difference in readings as recorded on a strip chartbetween the two total pressure gauges. This patent also demonstrates theuse of acoustics by using a microphone for recording the sounds that maybe made by escaping fluid between two sealing elements carried by thepig.

As can be seen, the prior art for leak detection in pipelines utilizesdifferential pressure measuring means, microphones or total pressurerecordings in order to detect leaks inpipelines.

SUMMARY OF THE INVENTION The present invention advantageously providesan apparatus and method for making internal surveys of pipelines, inwhich instruments continuously monitor the difference in the flow ratethrough two orifice plates, disposed at each end of the apparatus.

An even further advantage of the present invention is providing anapparatus in which the difference in flow rate through the two orificeplates is recorded as a function of time and/or distance indicating anyleaks in the line by a change in signal that exists for a specified timeduration, or for a specified distance of travel.

DESCRIPTION OF THE DRAWING The nature of the present invention will bemore fully appreciated with reference to the drawing in which:

The FIGURE shows a diagrammatical view of an embodiment of the presentinvention for detection of small leaks in a pipeline and simultaneouslyrecording said leak.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the FIGURE, there isshown a device according to the invention being propelled through apipeline 10 in the direction of flow as indicated by the arrow A. As thedevice passes through pipeline 10, sealing members 11 at each end offrame member 13 tend to resist movement because of the snug fit againstthe inner wall of the pipeline l0, and as a result there is a smallpressure drop across the device. The resulting pressure drop ordifferential causes a part of the flow (arrow B) to pass through thedevice by way of holes 18 in first and second flow sensing means whichare shown as orifice plates 12 and 12 at each end of the device. Orificeplates 12 and 12' can easily be replaced with flow nozzles, venturimeters or flow meters and not depart from the intent or scope of thepresent invention. A sensing port 43 is disposed on the downstream sideof the first orifice plate 12 and sensing port 44 sense the pressure oneach side of the forward or first orifice plate 12, these two pressuresare then fed to a differential pressure sensing means 20 by way ofsensing lines 14 and 15 respectively. The resulting difference inpressure is then fed to another differential pressure sensing means 21by means of line 31. A second orifice plate 12' at the rear of thedevice has a similar set of sensing ports 43' and 44 which are in fluidcommunication with sensing means 22. The difference in pressure is fedto means 21 by way of line 32. Theoretically, under ideal conditions,the flow rate through each orifice plate 12 and 12' would be equal sothat the two pressures sensed by the differential pressure sensingdevice 2 1 (lines 31,32) would be equal and the output from means 21would be zero. In actual practice, however, it is unlikely that thiswould be true, due to different volume of fluid slippage past thesealing members 11 and the partial plugging of the holes 18 and 18' inthe orifice plates 12 and 12'.

Again, referring to the FIGURE, each sealing member 11 is secured to theframe member 13, by a flange 26, a ring 35, and a plurality of screws 34at each end of the frame member 13. The cylindrical shaped members 27are secured to the frame member 13 by welds 28 on the outer diameter ofeach member 27. Each member 27 has a bore 40 therethrough and is furtherprovided with a shoulder 41 for orifice plate 12 to butt against. A snapring 33 or similar device retains the orifice plate 12 in place afterinstallation. Each member 27 is further provided with sensing ports 43and 44, one being disposed on each side of the orifice plates 12. Ob-

viously there are many other embodiments of these same members whichwill accomplish the purpose of this invention.

In one embodiment of the present invention, the measuring or recordingmeans 25, mounted on frame member 13 records the output signal from thedifferential pressure sensing means 21 as a function of the distancetravelled through the pipeline 10. As the device travels through thepipeline l0, disturbances, such as welds, cause variations in the flowrates through the respective orifice plates 12, and the correspondingoutput signals from sensing means 21. However, there is only onecondition where the change in the output signal from sensing means 21will be of a duration corresponding to the distance between the sealingmembers 11 disposed at each end of frame member 13. This conditionoccurs when flow is either entering or leaving the volume encompassed bythe pipeline 10 between the sealing members 11 at each end of the devicethrough an aperture other than the holes 18 in each orifice plate 12 orslippage past sealing members 11. Therefore, the detection of leaks inthe pipeline 10 is accomplished by measuring and/or recording theduration of the change in the output signal of sensing means 21, whichchange is a measure of the difference in the respect-ive flow ratesthrough each orifice plate 12.

In a second method utilizing the apparatus of the present invention forthe detection ofleaks, the recording means 25 would record the outputsignal from sensing means 21 as a function of time. When used in thisfashion, the device would be pumped through the pipeline 10 at aconstant velocity so the distance between the sealing members 11 wouldbe traversed in a known increment of time. Using this embodiment of theinvention any leaks in the pipeline 10 would be indicated by a change inthe output signal from sensing means 21 that would be of a durationequalling the increment of time hereinbefore described.

Using either of the previously described methods, the detection andlocation of a leak or leaks in the pipeline 10 can be determined fromthe distance travelled between the point of insertion into pipeline land the point at which the change in signal of the required durationoccurs.

When the output signal from sensing means 21 is recorded as a functionof the distance travelled through the pipeline 10, the location of theleak or leaks may read directly from the record. However, when thesignal from 21 is recorded as a function of time, the distance from thepoint of insertion is calculated from a record of the rate of flowthrough the pipeline 10.

Further, the determination of leak location may be further refined bymeasuring the distance from known points ofinjection into or deliveryfrom the pipeline 10, since either of these conditions will be recordedin much the same manner as a leak. Location ofleaks may be furtherrefined by marking the record at desired locations by external meanssuch as magnets, encircling coils, or other means well known in the art.

The required time of duration of the change in signal from the sensingmeans 21 will vary depending upon the length of leak detector and thevelocity at which the detector is propelled through the pipeline 10.Therefore, the specified time will vary and one skilled in the art wouldnot have difficulty in specifying the required time depending upon anyparticular application of the leak detector.

The recording means 25 may record continuously and the resulting recordhe examined visually, or instrumentation may be installed to filter outall signals from 21 except those of the appropriate required duration toindicate leaks, and only these signals recorded as functions of distanceor time. Or, the recording means may be magnetic tape or a similardevice, and the recording examined and analyzed by a computer.

Only one embodiment of the present invention has been shown, but itwould be obvious to substitute two diaphragm-type electricalpressure-sensitive devices having a variable output voltage and a bridgecircuit for the differential pressure sensing means 20. A similarsubstitution would also be made for sensing means 22. The sensing means21 would be replaced with a bridgetype circuit. Using this method wouldbe equivalent to the previously described preferred embodiment.

in some circumstances involving clean fluids and smooth internal pipesurfaces, the quantity of fluid leaking may be determined by examinationof the record. Careful examination of the record will also disclosecertain other types of pipeline damage, such as dents in the pipe wall.

I claim as my invention:

1. An apparatus for detecting leaks in a pipeline, said apparatus beingdisposed to be propelled through the pipeline by the fluid flowing inthe pipeline, said apparatus comprising:

a frame member;

seal means attached at each end of said frame member, said seal meansbeing adapted to sealably engage the inside wall of said pipeline, saidseal means being spaced to isolate the portion of the pipeline betweensaid spaced seal means;

flow means disposed in each of said seal means for establishing a fluidflow path between opposite ends of said frame member, said flow pathcommunicating with the portion of the pipeline isolated by said spacedseals;

first and second flow sensing means, one flow sensing means beingmounted at each end of said frame member, said flow sensing means beingmounted to detect the fluid flow through each of said flow means;

means for comparing the flow through each of said flow sensing means,said comparing means being adapted to receive a signal from each of saidflow sensing means and having an output signal equal to the differencein signal from said first and second flow sensing means; and

recording means for recording said output signal from said comparingmeans, said output signal being an indication of a leak in said pipelinewhen said signal exists for a specified duration of time.

2. The apparatus of claim 1 wherein said first and second flow means areorifice plates disposed in the ends of said frame member.

3. The apparatus of claim 2 wherein said means for comparing the flowthrough each flow sensing means comprises:

a first and second differential pressure measuring device, said devicesbeing adapted to measure the difference in pressure on each side of saidpair of orifice plates; and

a third differential pressure measuring device, said device comparingthe output signal from said first and second differential pressuremeasuring devices, said third differential pressure measuring devicebeing in fluid communication with said first and second devices. 4. Theapparatus of claim 1 wherein said recording means records said outputsignal as a function of time. 5. The apparatus of claim l wherein saidrecording means records said output signal as a function of distancetravelled through said pipeline.

6. A method of detecting leaks in a pipeline wherein a device ispropelled through the pipeline by the flow of fluid therethrough, saidmethod comprising the steps of:

isolating a section of the pipeline between a first and second sealmeans; establishing a fluid flow through said first seal means into saidisolated section of the pipeline and then out said second seal means;measuring the rate of flow through a first seal means disposed at theforward end of said device; measuring the rate of flow through a secondseal means disposed at the rear of said device; and comparing thedifference of the rates of flow through said first and second sealmeans, said difference being an indication of a leak in said pipelinewhen said difference exists for a specific period of time. 7. The methodof claim 6 further including the step of recording the difference in therates of flow through said first and second seal means.

1. An apparatus for detecting leaks in a pipeline, said apparatus beingdisposed to be propelled through the pipeline by the fluid flowing inthe pipeline, said apparatus comprising: a frame member; seal meansattached at each end of said frame member, said seal means being adaptedto sealably engage the inside wall of said pipeline, said seal meansbeing spaced to isolate the portion of the pipeline between said spacedseal means; flow means disposed in each of said seal means forestablishing a fluid flow path between opposite ends of said framemember, said flow path communicating with the portion of the pipelineisolated by said spaced seals; first and second flow sensing means, oneflow sensing means being mounted at each end of said frame member, saidflow sensing means being mounted to detect the fluid flow through eachof said flow means; means for comparing the flow through each of saidflow sensing means, said comparing means being adapted to receive asignal from each of said flow sensing means and having an output signalequal to the difference in signal from said first and second flowsensing means; and recording means for recording said output signal fromsaid comparing means, said output signal being an indication of a leakin said pipeline when said signal exists for a specified duration oftime.
 2. The apparatus of claim 1 wherein said first and second flowmeans are orifice plates disposed in the ends of said frame member. 3.The apparatus of claim 2 wherein said means for comparing the flowthrough each flow sensing means comprises: a first and seconddifferential pressure measuring device, said devices being adapted tomeasure the difference in pressure on each side of said pair of orificeplates; and a third differential pressure measuring device, said devicecomparing the output signal from said first and second differentialpressure measuring devices, said third differential pressure measuringdevice being in fluid communication with said first and second devices.4. The apparatus of claim 1 wherein said recording means records saidoutput signal as a function of time.
 5. The apparatus of claim 1 whereinsaid recording means records said output signal as a function ofdistance travelled through said pipeline.
 6. A method of detecting leaksin a pipeline wherein a device is propelled through the pipeline by theflow of fluid therethrough, said method comprising the steps of:isolating a section of the pipeline between a first and second sealmeans; establishing a fluid flow through said first seal means into saidisolated section of the pipeline and then out said second seal means;measuring the rate of flow through a first seal means disposed at theforward end of said device; measuring the rate of flow through a secondseal means disposed at the rear of said device; and comparing thedifference of the rates of flow through said first and second sealmeans, said difference being an indication of a leak in said pipelinewhen said difference exists for a specified period of time.
 7. Themethod of claim 6 further including the step of recording the differencein the rates of flow through said first and second seal means.